Because of the importance of integrated optics in the telecommunication industry, a great deal of effort has been expended to reduce insertion loss associated with coupling a light between integrated optical components and fiber links, to the lowest possible level and with reasonable expenses. Such components are on-fiber modulators, switches, couplers, and distribution devices. There also exists a need for a fiber optic coupler which is tunable for high accuracy, inexpensive, easily fabricated and one which can be used without the problems of coupling the light signal from or to the optical link. This invention is an improvement on U.S. Pat. No. 5,060,307.
have invented such an on-fiber tunable coupler which uses two optical fibers, each having a small region from which the cladding material has been removed. The fibers are then placed parallel and close to each other before they are coated with an active multilayer materials structure in the region of uncladded fibers. The multilayer coating is constructed of at least three layers, a conductive layer coated on the surface of the fiber cores, an electrooptic material coated on the top of the conductive layer (the inner electrode) and a conductive layer coated on the top of the electrooptic material acting as the outer electrode. The advantage of this multilayer coating is that it is sensitive to electromagnetic fields and will satisfy the condition that in the presence of an external electromagnetic field, the optical properties of the modified region will change.
Another advantage is achieved by tuning the optical properties of the electrooptic material which is controlled by applying an external electromagnetic field to the device across the region of coating with the active multilayer materials. The device of this invention can be used as an electromagnetic field sensor for determination of the applied external signal. The active medium or the coated materials in the region of the unclad fibers controls energy transferred between the fibers and provides modulation of the signal transmitted in each optical fiber when an external signal is applied.
Other advantages will appear hereinafter.